The Sallen-Key architecture is also known as a voltage control voltage source (VCVS) architecture. It is one of the most widely used filter topologies in circuit designs. The Sallen-Key architecture is a filter architecture designed to provide flat gain response in the pass band. Source-follower-based Sallen-Key filters are widely used in baseband architectures and radiofrequency (RF) architectures. A typical example is the use of a biquad source-follower-based Sallen-Key filter in a transmit baseband path for DAC (digital-to-analog conversion) image rejection. A source follower-based Sallen-Key architecture provides lower distortion, wider bandwidth and lower power compared to an operational amplifier-based buffer.
A source follower, also known as a common drain amplifier, is a circuit configuration used in circuit designs to provide a voltage buffer or to transform impedances. In general, a source follower circuit provides high input impedance, low output impedance, and a voltage buffer. A Sallen-Key architecture is a second-order active filter, and its external filter characteristics include a finite input impedance and a small output impedance. Sallen-Key filters can be designed as a low-pass, band-pass, or high-pass filters. A higher filter order can be achieved by cascading two or more Sallen-Key circuits.